METHODS: This is a population-based, cross-sectional study. Among 5053 enumerated children aged 5-15y in Guangzhou, 3729 (73.8%) children aged 7-15 with successful cycloplegic auto-refraction (1% cyclopentolate) and a reliable visual acuity measurement were included. Ocular measurement included external eye, anterior segment, media and fundus and cycloplegic auto-refraction. Primary outcome measures included the relationship between severity and subtypes of astigmatism and the prevalence of visual impairment. Three criteria for visual impairment were adopted: best-corrected visual acuity (BCVA) ¡Ü0.7, uncorrected visual acuity (UCVA) ¡Ü0.5 or <0.7 in the right eye.

    RESULTS: Increases of cylinder power was significantly associated with worse visual acuity (UCVA: ¦Â=0.051, P<0.01; BCVA: ¦Â=0.025, P<0.001). A substantial increase in UCVI and BCVI was seen with astigmatism of 1.00 diopter (D) or more. Astigmatism ¡Ý1.00 D had a greater BCVI prevalence than cylinder power less than 1.00 D (OR=4.20, 95%CI: 3.08-5.74), and this was also true for hyperopic, emmetropic and myopic refraction categories. Oblique astigmatism was associated with a higher risk of BCVI relative to with the rule astigmatism in myopic refractive category (OR=12.87, 95%CI: 2.20-75.38).

    CONCLUSION: Both magnitude and subtypes of astigmatism influence the prevalence of visual impairment in school children. Cylinder ¡Ý1.00 D may be useful as a cutoff for clinically significant astigmatism.